U.S. Pat. No. 4,015,686 discloses a multi-stage lift which has been in commercial production for many years. In this lift the stages comprise like extruded aluminum mast sections which interfit in front to back relation and are separated in the front to back direction by guide rollers. These rollers track between laterally extending flanges at the back of each mast section and interfitting front flanges on the adjoining mast section. These front flanges extend inwardly as part of front channels which face inwardly toward one another. Stub shafts for the rollers extend through the central wall of these front channels. The front channels and interfitting back flanges of adjoining mast sections extend from central hollow columns of generally rectangular cross-section. A reeving system for a cable from a rear winch to a front carriage on the mast includes tilted pulleys adjacent the bottom of the mast sections and laterally extending pulleys at the front of the central column portions of the mast sections.
The described prior art mast construction does not provide for any roller alignment of the mast sections from side to side while they are extended and retracted. Such alignment is only provided by friction contact by the ends of the front-to-back guide rollers with the adjacent outer side faces of the adjoining mast section. Accordingly, a major objective of the present invention is to provide an improved mast configuration which will provide side-to-side roller contact between adjoining mast stages as well as front-to-back roller contact.